The invention herein relates to the projection of optical images from a source to a display screen and specifically is directed to a method and apparatus for forming a projectable transparency from an image source and providing large screen display of said image, the transparency being formed on an electrophotographic film member.
Large scale display of photographic images is frequently utilized in conjunction with explanation of the data represented by said images before large groups of viewers. Ordinary photographic images are carried in the form of mounted transparencies and are introduced to projecting apparatus which project enlarged images onto a viewing screen. Often the large source carries information which is required to be displayed in enlarged form within a very short time span subsequent to its origination. Images displayed on cathode ray tube display units such as the video signal transmitted to a television receiver or information fed to an oscilloscope desirably are displayed on an enlarged scale for the presentation of important highly detailed information to a large audience. Government agencies, financial institutions and scientific gatherings are examples of such users. At present, considerable problems are encountered in achieving desirable large screen display from the aforementioned image sources. It is the practice to apply such images to strip material and process the same with conventional photographic techniques so that the information may be projected in enlarged condition upon a screen. With all presently known techniques, there is a substantial delay time between the origination of the image and the completion of the required transparency thereof to enable projection of that image. Conventional photographic film techniques require more processing time than electronic techniques such as videotaping but the enlargement and display of videotaped information requires complex and highly expensive apparatus.
Accordingly, it would be highly desirable to provide a method and apparatus for effecting large scale screen display of images from a source in which the processing time is materially reduced to a degree that the display can be projected "in real time," that is, almost instantaneously as derived from the source and further, it would also be desirable to effect such large screen display utilizing relatively inexpensive equipment, at substantially reduced frame by frame costs over conventional methods and apparatus and with a speed to provide a cinematographic display effect, if desired.
Another problem includes the present inability to provide high resolution images from sources of relatively low light intensity. Images received on a cathode ray tube display unit generally are of low intensity making photography difficult without unusual photographic conditions and very fast photographic film. Enlargement for display involving magnification of a substantial order also enlarges imperfections to the same degree. Resolution of the basic image must be of equal order relative to the resolution of the enlarged image. This factor, taken with the low intensity of the CRT image makes extremely difficult, if not impossible, photographic reproduction and subsequent large screen display of images of this character.
The advent of the electrophotographic film of the copending applications makes reproduction of images onto electrostatic members feasible and highly economical. Such electrophotographic film is a highly flexible, high speed, high gain, high resolution material with a hard and abrasion resistant surface. In addition, since the film is so fast and sensitive, it can respond quickly and easily even to the low light intensity of a cathode ray tube display unit image so as to provide excellent projectable images with a good gray scale. In addition, there is the capability for enhancing the received image forming a projectable transparency carrying an improved image over that received from the cathode ray tube display unit source.